Frictional Non Rocking Damped Base Isolation System To Mitigate Earthquake Effects On Structures

ABSTRACT

The system described herein consists of a seismic isolator and a damping device. The system is used to isolate structures from seismic forces and further reduces transmitted forces via the seismic isolator to structure. 
     The isolator has a spherical base fixed to ground, middle part that responds to the moving base by rotating around the centre of a small concave or convex, causing the superstructure to move upwards and downwards vertically, and a top part connected to the superstructure and the isolator middle part. 
     The damping device consists of horizontal seismic force filter, springs, dampers and a vertical force transferor beam. 
     Structures seismically isolated with the system herein may be protected to adequate amounts that allow minimal or no damages to the superstructures. That means continuous serviceability during and aftermath becomes achievable for the very most of the earthquakes and site characteristics combinations.

TECHNICAL FIELD

Civil Engineering, Structural Engineering, Earthquake Engineering.

BACKGROUND

The system is a part of the devices that intended to protect structures from earthquake effects some of these devices attenuate the imparted forces to the superstructures. Other devices minimize the forces to be imparted to the superstructures and thus they are called seismic isolators. The system described herein is a part of the both types of seismic protecting devices where it protects structures from earthquake effects by isolating the structures and minimizing the transmitted forces via the Mary Grace Seismic Isolator and attenuates further the remaining transmitted forces by means of the Mary Grace Damping Devices.

Friction Pendulum System or FPS is the most relevant device to the isolator described herein, while there is no counterpart to the Damping device, although some parts thereof are common, such as the viscous dampers and springs. However, the isolator described herein, has different middle part and functions very different from that of the FPS. Where, the isolator described herein:

-   -   1—The isolator described herein doesn't rock while the FPS does         rock.     -   2—Highly reduces horizontal displacement seismic responses of         the superstructures due to its middle part shape and allowable         extreme smoothness of the contacting surfaces.     -   3—Unlike FPS, the Mary Grace Isolator horizontal response is         independent from earthquake frequency where it prevents         superstructure horizontal rocking. This rocking becomes         dangerous in case of resonance between the FPS and ground motion         frequencies,     -   4—Prevents superstructures from moving when subjected to wind         loads while this is not the case in the FPS.     -   5—Allows high isolation efficiency by allowing extremely low         friction factors of the contacted surfaces, where this is not         the case in the FPS because the friction reduction is limited by         wind loads forces that can move the superstructures over the FPS         base.     -   6—Furthermore, FPS causes high stresses on the contact surfaces         with the concaves, that causes maintenance problems, while         contact stresses in the Mary Grace isolator are much less. As a         result, maintenance process becomes less demanding.         Then, the isolator described herein is to be used effectively         for very strong and different frequency earthquakes,         transferring much less forces and displacements to the         superstructure in comparison with FPS, including resonance         cases.

Additional dissipation of energy is provided by the damping device that can have a viscous damper, or other types of dampers. This dissipation helps to further reduce transmitted energy to superstructures because of the special design of the damping device connections that provide for such damping of transmitted energy.

The system described herein can be fabricated with contacted surfaces have as low friction coefficients as can be generated by Tribology industry of solid lubricants. This ability provides for transmitted seismic forces to superstructures to be small enough and for wind forces to be the dominant forces in structural designs that are, in most of the cases and codes, much less demanding and less stringent.

Lastly, because of low transmitted forces, displacements and then drifts and interstory forces, structure continuous serviceability can be assured in most of the isolated structures by providing flexible connections with the main sanitary and water pipes and securing complete separation between ground and the superstructures but the flexible connections and the system described herein. Minimal or no damages to claddings and other non structural elements is expected in superstructures isolated by the Mary Grace System described herein.

SUMMARY OF INVENTION Invention in the Isolator:

As described in the comparison between the FPS and the Mary Grace Isolator, the innovative parts in the Mary Grace Base Isolator are the middle parts that function differently from that of the FPS. Where, the isolator described herein:

-   -   1—Doesn't move with the wind forces. This wind resistance allows         using contacting surfaces with the lowest possible friction         factors that might reach 0.01 or less. Then the transmitted         forces would be much less than that transmitted with the FPS,         and a very small fraction of the earthquake forces.     -   2—Earthquake frequency and site characteristics don't affect         much the performance of the isolator and then the transmitted         forces to the superstructures. That because the isolator         described herein doesn't rock.     -   3—Greater contact surfaces between the convexes and concaves         make the functional stresses much less and maintenance process         becomes less demanding.     -   4—The movement of the superstructures are up and down instead         from side to side that because the ability of the middle part to         rotate around the center of the small concave-convex connection         that is different from the center of the base concave.

Invention in the Damping Device:

-   -   1—Mary Grace Damping device can damp seismic forces without         inducing more significant forces into the isolated         superstructures. That is possible because of the innovative         connection between the superstructure and ground. The special         connection of steel balls and two containers allows to attenuate         seismic forces further before affecting the whole structure as         it connect one isolated object (superstructure) to an external         object (ground). As a matter of fact the balls transmit only the         vertical forces, while horizontal seismic forces range from         0.001-0.005 of the spring vertical forces. The lowest number can         be reached by providing very smooth surfaces contact the steel         balls and by making the steel balls themselves very smooth.         Furthermore, the induced horizontal forces can be reduced         further by sloping the dampers while the horizontal         displacements can be reduced by sloping the springs.     -   2—The application ability of viscous damping, using the Mary         Grace Damping devices, to the isolated structures, by means of         FPS, allows to avoid resonance impacts on the superstructures,         where incorporating viscous dampers into the isolated structures         (internal damping) doesn't improve the situation and attenuate         the vibration, that because of the vibration amplitude reaches         infinity in the resonance vicinity. On the other hand adding         external dampers without the special connection of the balls         increase significantly the induced seismic forces to the         superstructures.

Functions of the Embodiments:

The Mary Grace Base isolator or briefly isolator is used to isolate buildings, bridges, silos, factories and other structures, being made from concrete, steel, wood or other materials, from earthquake effects when are susceptible to earthquakes, so that it protects these isolated structures, from being highly damaged or failed, by means of reducing transmitted forces to superstructures and displacements thereof.

The isolators are installed under structure foundations, footings or columns (see FIGS. 1A, 1B, 2A and 2B) one isolator under each column, foundation or footing. The upper part of the isolator is fixed to a superstructure and the bottom part is fixed to a ground footing spread the weight of foundation into ground. Ground footings become a source of earthquake forces and displacements during an event. Nevertheless, the foundations or columns on the upper side, and therefore the superstructure, receive much smaller forces and displacements from the isolator. There must be no rigid connections between the superstructure and ground other than the isolators and may be the Mary Grace damping device, if used, in order to ensure the highest possible level of protection.

An isolator can work alone or in combination with a damping device described herein. When an earthquake hits an isolated structure, the superstructure moves slightly up and down. The magnitude and frequency of the vertical movements depends on the design earthquake characteristics and the isolator's dimensions, geometry and materials.

Mary Grace Base Isolator Description:

A Mary Grace Isolator or briefly an isolator consists of three main parts:

1. Base: it is the first part, 1, in FIGS. 1A, 1B, 2A and 2B. A base has one flat side connected to a ground footing that is the fifth part, 5, in 1A, 1B, 2A and 2B, while the other side is spherical part (concave) has two radii, vertical radius R_(v) and horizontal R_(h), that are calculated from the requirements for self returning to the stationary position at the lowest point of the base, and from the largest displacements expected in a region for the most credible design earthquake respectively. The concave surface must have the lowest possible friction coefficient so it induces smallest possible forces to the isolated superstructures. 2. Middle part: it is the second part, 2, in FIGS. 1A, 1B, 2A and 2B. This part offers two main advantages that make the isolator unique in the whole world. First special advantage is that it provides for non rocking response of the superstructure. Instead, the superstructure moves vertically because of the middle part rotation around the centre of small convex -concave joint that connects the middle part to the upper part of the isolator. Another very especial characteristic is that it prevents the superstructure from moving by wind forces no matter how smooth are the contacted surfaces of the base and the middle part of the isolator. See FIGS. 1A, 1B, 2A and 2B). The middle part contacts the isolator base via its bottom smooth, low friction spherical disk surface. This surface has the same vertical radius as that of the isolator base for the whole surface (See FIGS. 1A and 2A) or part of it as in FIGS. 1B and 2B where the Middle part bottom surface has the vertical radius in its center part and different smaller vertical radius for the surrounding parts. 3. Top part: it is the third part, 3, in FIGS. 1A, 1B, 2A and 2B. This part has bottom side that fits the middle part top part. This part has an upper side that is flat and fixed to a superstructure that is the fourth part, 4, in the FIGS. 1A, 1B, 2A and 2B.

Mary Grace Damping Device Function:

When Mary Grace Damping Device works in combination with Mary Grace Isolators, it further attenuates movements of the superstructure by means of its springs and dampers. Dampers absorb energy to soften the superstructure vibrations, while springs store strain energy and helps restricting further horizontal displacements and helps returning the system to its stationary point aftermath.

When a Mary Grace Damping Device works with a Friction Pendulum System isolator (FPS), it highly attenuates the resonant response in case of FPS and Earthquake frequencies are close. In addition, Mary Grace Damping Device reduces both vertical and horizontal displacements of a superstructure isolated by FPS devices.

Mary Grace Damping Device Description:

The Mary Grace Damping Device consists of five main parts, See FIGS. 3, 4 and 5:

1. Base, that is the first part, 1, in FIGS. 3, 4, and 5. It is a flat disk with constant height perimeter wall. A Base looks like a short barrel with no cover. The Base is attached to a superstructure (Part 7) via dampers and springs, parts 5 and 6 in FIGS. 4 and 5. The Base can be fixed from bottom directly to superstructure as in FIG. 3., or via dampers and springs as in FIGS. 4 and 5, Mary Grace Damping Device Base contains steel balls that are restrained in their ultimate movements by the Base perimeter. Consequently, the Base horizontal radius must be great enough to prevent any potential crushing between the cover and the Base. The base radius can be calculated from the maximum displacement of all earthquakes in a considered region. 2. Cover, is the third part, 3, in FIGS. 3, 4 and 5. It is similar in shape but smaller than the base, and placed upside down. The cover contacts steel balls from bottom and is connected indirectly to ground from the top via steel beam (part, 4, in the FIGS. 3, 4 and 5) and two steel columns (part 9) as in FIGS. 4 and 5. The Cover can be connected to ground via a steel beam, dampers (part, 5,) and springs (part, 6,) as in the FIG. 3. However, the last connection it's not the preferable connection. 3. Middle Part (3), in FIGS. 3, 4 and 5 consists of steel balls transfer mainly vertical displacements from superstructure to dampers and springs via the Base, balls and Beam as in FIG. 3, or directly to the dampers and springs as in FIGS. 4 and 5. As a result, dampers and springs move certain compatible displacements to that of the superstructures, dissipating energy and attenuating movement accelerations and velocities, and thus softening the responses of superstructures isolated by FPS or by Mary Grace Isolators, 4. Beam that is the fourth part, 4, in FIGS. 3, 4 and 5 is usually to be made of steel and can be made of other materials. It connects the Mary Grace Damping Device to ground via dampers and springs as shown in FIG. 3 or by columns as seen in FIGS. 4 and 5. The beam function is to transfer relative vertical displacements of the superstructure to dampers and springs. 5. Dampers , that are the fifth part, 5, in FIGS. 3, 4 and 5, are attached to the Base of one side and to a superstructure in the other side as per FIGS. 4 and 5 or attached to a steel beam from one side and to ground from the other side as in FIG. 3. Dampers function is to attenuate the superstructure motions. Dampers can be viscous or any other types such as those using Magnetorheological fluid. 6. Spring is the sixth part, 6, in FIGS. 3, 4 and 5. A spring attached to the Base of one side and to the superstructure in the other side as per FIGS. 4 and 5 or attached to the steel beam from one side and ground from the other. Springs should have sufficient stiffness related to damping ratio, Earthquake and structure characteristics. The angles that might springs and dampers make with a ground (Horizon) can be right angle, 90, as illustrated in the FIGS. 3, 4 and 5. or less than 90 as it's not shown in these Figures. The inclined connection might be more advantageous in case of using the Mary Grace Damping System in combination with FPS.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Mary Grace Isolator drawings are illustrated in FIGS. 1A and 1B and FIG. 2A and 2B. The numbers in these figures are as follows: 1) Base. 2) Middle part, may have a cylindrical neck and a convex as in FIGS. 1A and 1B, or cylindrical neck and concave (as in FIG. 2A and 2B) in the top of the Middle part. 3) Upper part, may have a cylindrical neck and concave (as in FIGS. 1A and 1B) or a cylindrical neck and convex (as in FIG. 2A and 2B) in the bottom of the upper part. 4) Footing in ground. 5) Superstructure column, foundation or footing.

Mary Grace Damping Device drawings are illustrated in FIGS. 3, 4 and 5. The numbers in these figures are as follows: 1) Base. 2) Steel Balls 3) Cover. 4) Steel (or other material) Beam. 5) Dampers. 6) Springs. 7) Superstructure beam, column, foundation or footing. 8) Ground Footings. 9) Columns 

1. A steel, metal or other material device as shown in FIGS. 1A, 1B, 2A and/or 2B. This device consists of a base, part 1 in FIGS. 1A, 1B, 2A and 2B. The base has bottom flat side connected to a ground footing, part 4 in FIGS. 1A, 1B, 2A and 2B, and top side is spherical (concave) contacts the middle part of the Isolator. The base might be surrounded by an edge around its circumference as a displacement restrictor for extremely large displacements resulted from too strong and non foreseeable earthquake magnitudes. The edge might be covered by rubber. Base horizontal radius, R_(h), is calculated from design earthquake maximum displacements where the middle part should not hit by the edge of the base during an event. While the vertical radius, R_(v), is calculated from the required gravity forces to return the isolator and then the superstructure to its stationary point at the centre of the base concave when an earthquake stops. After an earthquake stops the expected permanent displacement of the middle part from the stationary point can be as small as ±F×R_(v)where R_(v) is the vertical radius of base concave and F is the coefficient of friction between the base and middle part surfaces. The base concave surface must be so smooth. In other words, the coefficient of friction must be so low. This can be achieved by preferably using solid lubricants that include but not limited to Disulfides Molybdenum, MOS2. Other lubricants may be used to have these surfaces smooth.
 2. Middle part of the Mary Grace Isolator is a disk cut from a thick spherical surface that has an outer vertical radius equal to the vertical radius of the base concave in claim (1) See FIGS. 1A and 2A. This middle part may have two vertical radii as shown in FIGS. 1B and 2B. First vertical radius is the same vertical radius of the Base concave, R_(v), and it is used for the central part of the Isolator Middle part. The other vertical radius should be smaller than Rv, in order to allow decreasing or tapered space between the Base and the Middle part. The gradually decreasing space provides for gradual application of horizontal forces from the Base on the Middle part. The gradual application of forces provides for much less jerk responses of the isolator. The Middle part disk is connected to a convex, FIGS. 1A and 2A, or concave, FIGS. 2A and 2B, of smaller vertical radius than that of the disk itself. The small concave or convex is situated in the top surface centre of the disk. The convex or concave can be connected directly to the disk or through a cylindrical neck. The middle part is connected to the top part of the isolator through convex-concave joint as in FIG. 1A and 1B, or concave- convex joint, as in FIG. 2A and 2B. The convex-concave or concave- convex connections allow the middle part to rotate around the rotation centre of its top convex or concave. Most of the small convex surface has a same radius of the concave of the upper part. While near the edges between the small convex and concave surfaces, the convex surfaces have smaller radius than the concaves as shown in the FIGS. 1B and 2B, the smaller radius makes decreasing or tapered space between the small concave and small convex as shown clearly in FIGS. 1B and 2B blow ups. The contacted surfaces between the small convex and concave must be adequately so smooth. As a result the rotated convex of the middle part be accommodated into the concave and allows contact surfaces between the convex and concave to be great enough to have stresses less than allowable stresses of the contacted surfaces. Similarly, the middle part concave must have the same radius of the upper part convex for most of its surface and slightly greater radius near the edges with the upper part convex so that the middle part can rotate easily about its top small convex center.
 3. Third part of the Mary Grace Isolator is a disk has a flat top side and has bottom side that fits well the upper part of the isolator Middle part. Thus, the third part must have concave or convex surface to contact and fit the middle part convex or concave surfaces respectively. The third part has upper side that is flat and fixed into superstructure. See FIGS. 1A, 1B, 2A and 2B. Tapered space described in claim 3 between the small concave and convex can be made by changing the Upper part convex, near the edges with the Middle part concave, to a smaller radius than the convex main part or by making the Upper part concave, near the edges with the Middle part convex , of a slightly greater radius than the convex. For the Mary Grace Damping Device described above, what claimed are:
 4. The Mary Grace Damping Device a device acts as a damping machine attenuate response vibrations of the isolated superstructures. The damping device should be connected to both superstructure and ground. The damping device has a base, that is the first part, 1, in FIGS. 3, 4, and
 5. A Damping Device Base is a flat disk with constant height perimeter wall. The Base looks like a short barrel with no cover. The Base is attached to superstructure (Part 7) via dampers and springs, parts 5 and 6 in FIGS. 4 and
 5. The Base may be fixed from bottom directly to superstructure as in FIG.
 3. The Mary Grace damping device Base upper side contains steel balls that are restrained in their movements by the cover perimeter.
 5. Cover, is the third part, 3, in FIGS. 3, 4 and
 5. It is similar in shape but smaller than the Base, and placed upside down. The cover contacts steel balls from bottom and is connected indirectly to ground from the top side via steel beam (part, 4, in the FIGS. 3, 4 and 5) and two steel columns (part 9) as in FIGS. 4 and 5, or via a steel beam, dampers (part, 5,) and springs (part, 6,) as in the FIG.
 3. 6. Middle Part (3), in FIGS. 3, 4 and 5 consists of steel balls transfer mainly relative vertical displacements from superstructure to dampers and springs. As a result, dampers and springs move certain compatible displacements to that of the superstructures relative displacements dissipating more energy and helping restoring the superstructure to its stationary point.
 7. Beam that is the fourth part, 4, in FIGS. 3, 4 and
 5. it is usually made of steel and can be of other materials. It connects the Mary Grace Damping Device to ground footings, part 8 in FIGS. 3, 4 and 5, via dampers and springs as shown in FIG. 3 or by columns as seen in FIGS. 4 and
 5. The Beam function is to help transferring the relative displacements from superstructure to dampers and springs and impose back the dampers and springs' reactions into the superstructure.
 8. Dampers and springs are the fifth and sixth parts respectively, 5 and 6, in the FIGS. 3, 4 and 5, they are attached to the Base of one side and to a superstructure in the other side as per FIGS. 4 and 5 or attached to the Beam from one side and to ground from the other side as in FIG.
 3. Dampers can be viscous or other types such as those using Magnetorheological fluid. Springs should be of sufficient stiffness in relation with used damping ratios and design Earthquake characteristics. Mary Grace Damping System to be used to idealize a structure performance response under a ground motion and smooth the vertical vibrations of the Mary Grace Isolator. In addition Mary Grace Damping System can be used in combination with FBS devices to restrict further the response displacements and attenuate the further the transmitted forces, especially in case of resonance. The angles that might springs and dampers make with ground (Horizon) can be right angle, 90, as illustrated in the FIGS. 3, 4 and 5, or less than 90 as it's not shown in the Figures. When a superstructure starts to move, it pushes the Mary Grace Damping Device Base upwards, FIG. 3, or it pulls the springs and dampers and the Damping Device Base upwards, FIGS. 4 and 5, subsequently the springs and dampers engage in attenuating the superstructure vertical vibrations and in returning the superstructures to its stationary position in smooth way when earthquake stops. While when the Mary Grace Damping Device is used with an FPS it further reduces horizontal displacements in addition it extremely attenuates the resonant response. 